The present invention relates generally to two-step pressure intensifying devices. More particularly, the present invention relates to clamps, vises, or other securing devices employing a two-step pressure intensifying device for securing workpieces.
Pressure intensification devices have been known and used heretofore for hydraulically powered machine tools such as punch presses. Typically, a low pressure air source is utilized to drive a driving piston having a relatively large cross-sectional area. The driving piston is connected to a driving rod having a piston head with a much smaller cross-sectional area. This smaller piston is driven against hydraulic fluid in a suitable sealed cylinder, resulting in intensification of pressure according to well-known laws of fluid dynamics. This simple type of one step or one stage pressure intensifying device is well-suited for many applications; however, a major problem experienced with this type of device is the relatively slow extension speed of the operative number.
In order to provide a suitable pressure intensifying device which not only greatly intensifies pressure available from a low pressure source, but also has a more rapid initial extension speed, two-step pressure intensifying devices have been developed.
One such two-step pressure intensifying device is shown in Canadian Pat. No. 1,052,234 issued to Mr. G. G. F. Smeets. According to the Smeets patent, a two-step pressure intensifying device is provided where low pressure is initially applied to hydraulic fluid by a relatively large cross-section area piston head. In the initial low pressure mode, a tool punch or other hydraulically operated machine part is rapidly moved by the large low pressure displacement of hydraulic fluid by the piston head. When the tool punch meets resistance by contacting a workpiece, hydraulic fluid bleeds past the piston head as the piston head is continually moved against the hydraulic fluid. The piston head is mounted on a suitable drive rod which has a body portion which serves as the second lower cross-sectional area high pressure piston. The drive rod body is connected to the piston head by a narrow neck.
With the punch tool contacting the workpiece, the drive rod moves continually downward until the drive rod body is sealed by a suitable seal as it enters the hydraulic fluid. The drive rod body, with its small cross-sectional area, then applies higher pressure to the hydraulic fluid to complete the desired punching or other high pressure process, at a lower speed. Although the two-step hydraulic pressure intensifying device as shown in the Smeets patent is suitable for punching operations or other situations where a large number of similarly sized workpieces are contemplated, these devices are not suitable for other applications where a large number of variably sized workpieces are encountered.
Specifically, it would be desirable to provide a suitable clamp or vise for securing workpieces of differing sizes wherein the vise included a two-step pressure intensifying device so that the vise jaws could be closed initially upon the workpiece very rapidly with the subsequent automatic application of high pressure to securely hold the workpiece during mechanical operations thereon. The Smeets type intensifier is not suitable for this purpose since the Smeets device is totally enclosed with the punch plug having limited travel.
It is therefore desirable to provide a suitable two-step pressure intensifying device for use in clamping or otherwise securing variously sized workpieces.
The two-step hydraulic pressure intensifying device should be suitable for use with a vise body or the like for clamping variously sized workpieces to support tables. Especially for clamping operations, it would be desirable to provide a two-step hydraulic pressure intensifier having a telescopic cylinder wherein the extension reach of the telescoping cylinder is maximized and where the telescoping cylinder is extended relatively rapidly by application of low pressure to hydraulic fluid within the cylinder followed by application at high pressure to hydraulic fluid within the cylinder at slower telescoping cylinder extension speeds when the workpiece is contacted and clamped.